The work of mapping radon sources on a large scale has been progressing, with large numbers of measurements of radon in homes made and mapped. Lognomal modelling of the data has allowed radon-prone areas to be mapped at 5 km resolution across most of the UK, and at 1 km resolution in areas that have been intensively measured. A method has been developed for transferring data on radon in homes in a given area in a way that preserves the detailed geographical information for correlation with geology without compromising the confidentiality of the radon results. Measurements have been made of radon levels in new and existing homes with various anti-radon measures. These have shown that new homes in radon-prone areas can be effectively protected by installing suspended concrete floors with vents for sub-floor ventilation and covered by a continuous membrane across the whole floor area. Such measures are not expensive and provide a high level of protection. Tests have been carried out in various existing homes and other buildings where radon remedial measures have been installed. In buildings with solid concrete floors, sub-floor sumps attached to extract fans have been shown to be highly effective and durable. Remedial measures on suspended timber floors have proved to be more problematical, but the provision of a continuous flow of air across the sub-floor space in often effective. Positive ventilation of homes using a fan blowing air in from the roof space has also proved to be effective in reducing radon levels in suitable homes. Tests in buildings where the natural under-floor ventilation has been increased by the provision of extra vents have shown this to be unreliable in reducing radon levels.